GB2143674A - High-pressure discharge lamp - Google Patents

Abstract

A discharge lamp comprises a discharge vessel 2 in an encasing bulb 3 with an intermediate vessel 13 arranged between them and fused at the top to the bulb 3. The intermediate vessel may be dome-shaped or tubular and may be of doped or coloured glass. It may be coated with one or more of the following: an IR-reflecting layer, a UV-reflecting layer, a fluorescent substance and/or a light diffusing layer. In addition it may be etched or sandblasted. In a modification (Fig. 3, not shown) the bottom of the intermediate vessel is supported by current lead-in wires (7''). <IMAGE>

Description

SPECIFICATION High-pressure discharge lamp The invention relates to a high-pressure discharge lamp, consisting of a discharge vessel with an ionizable filling, in which electrodes are sealed. The discharge vessel is surrounded by an encasing bulb and in addition - for example as a splinterproof protection, as a means for the absorption of heat or as a diffusion means - an intermediate vessel is provided which partially surrounds the discharge vessel.

In DE-OS 28 40 771, an intermediate vessel is used for heat absorption purposes. It is tubular in construction and surrounds the discharge vessel with slight spacing. In a lamp with a conventional frame construction, its securing is effected via two wire straps which are secured to one of the holding means, constructed in the form of current lead-in wires, for the discharge vessel.

A compact high-pressure discharge lamp, operated with direct current, is disclosed in DE-OS 30 28 405, wherein the discharge vessel is likewise surrounded by a tubular intermediate vessel. In this case, the latter is provided to prevent an Na diffusion out of the discharge vessel and serves as electrical shield and for this reason is connected to a predetermined voltage via a complicated frame construction - as can be seen from the Figures.

The present invention seeks to provide a simple means of securing an intermediate vessel in the encasing bulb of a high-pressure discharge lamp, which does not need any complicated or additional frame construction.

According to the present invention there is provided a high-pressure discharge lamp comprising a discharge vessel and an encasing bulb enclosing the discharge vessel, wherein an intermediate vessel is disposed therebetween, the intermediate vessel being fused with the encasing bulb.

In a preferred arrangement a discharge vessel pinched at one side is arranged in an encasing bulb pinched at one side. Since low-power high-pressure discharge lamps with a halide filling, such as are provided at present for use in residential and working fields, have an operating pressure of about 30 bar (3 x 1 06Pa), (this is distinctly higher than the 3 - 5 bar (3 - 5 x 105Pa) otherwise usual in such high-pressure discharge lamps with a higher power), an intermediate vessel for the purpose of protection from splinters increases the safety of use of the lamp. In the event of bursting of the discharge vesscl,the splinter particles either rebound from the intermediate vessel or, if their force is so high that even the intermediate vessel is penetrated, their velocity is reduced in the course of this so that in any case the outer bulb withstands the impact.

In addition, the intermediate vessel can be used for heat absorption or accumulation purposes or as a diffusion means.

For this purpose, this is provided with one or more UV-reflecting and/or IR-reflecting layers, a lightdiffusing coating and/or with a surface matted by etching or sandblasting. Sn-doped IN203 or Sio-Tio2 is suitable, for example, as an IR-reflecting layer.

The slight etching or sandblasting of the surface of the intermediate vessel has the effect that, due partly to total reflection, long path lengths of the radiation in the intermediate vessel occur and this radiation is absorbed to a greater extent by the intermediate vessel. This leads to a heating up of the intermediate vessel which in turn has an advantageous effect on the temperature of the discharge vessel.

Furthermore, it is possible to produce the intermediate vessel from doped glass, for example quartz glass doped with TiO2, or from coloured glass (filter glass). These glasses have the property of absorbing UV rays so that the glass heats up - as with the above-mentioned frosting likewise. These heat absorption measures may also be effected directly at the discharge vessel. For a required colour correction, an intermediate vessel of coloured glass is used, or it is coated with a fluorescent substance.

In one embodiment, the intermediate vessel is hood-shaped or dome-shaped in construction; in another advantageous embodiment it is tubular, and in each case it is fused, by its upper end, to the encasing bulb at or new: the apex of the latter. Both quartz glass and toughened glass are provided as materials for the various vessels.

It is also possible to use intermediate vessels thus arranged in lamps with a discharge vessel pinched at two sides in an encasing bulb pinched at one side.

In a further embodiment of the lamp, the current lead-in wires to the discharge vessel inside the encasing bulb are bent at an angle so that the intermediate vessel is supported. This has the advantage that a greater strength is achieved at the fusion point. A further advantage consists in that the outer current lead-in wires are situated wide apart.

As a result, surface leakage currents are prevented, the flash-over path is lengthened and the lamp can be ignited hot with a higher voltage surge.

The production of a metal halide high-pressure discharge lamp with an intermediate vessel, which is of hood-shaped construction in the first embodiment, is described in more detail below.

The encasing bulb needed is produced from a length of glass tube rotating about its longitudinal axis by heating a portion of tube up to the softening temperature and constricting the portion of tube by means of a roller moving in a direction perpendicular to the longitudinal axis. At this point, the encasing bulb now formed is also parted off from the rest of the tube - although a central aperture remains at the apex of the newly formed part. The hoodshaped intermediate vessel is produced in the same manner but from a glass tube, the diameter of which is smaller than that of the encasing bulb. The intermediate vessel is introduced into the encasing bulb until the outside surface of the upper end of the intermediate vessel and the inner face of the upper end of the encasing bulb bear against one another.

The two vessels are fused together at the contact point by means of a ring burner and then the exhaust tube is added and likewise fused to the encasing bulb.

In the production of a second embodiment of the lamp with the tubular intermediate vessel, the latter is introduced into the encasing bulb and fused to the encasing bulb by its upper encircling edge. Then the exhaust tube is added and likewise fused to the encasing bulb.

The finishing of the lamps of both embodiments is effected in accordance with known method steps.

The already completed discharge vessel is introduced into the intermediate vessel so that it is surrounded at least up to half the height of its pinch.

The encasing bulb is then pinched, sealing in the current lead-in wires and/or the molybdenum foils and the securing wire of the getter holding means, the internal volume of the encasing bulb is evacuated through the exhaust tube and the exhaust tube is then melted off. The lamp may additionally be provided with a base.

Three embodiments of the lamp according to the invention are illustrated in drawings and will be described in more detail below.

Preferred embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, of which: Figure 1 shows a metal halide high-pressure discharge lamp with a hood-shaped intermediate vessel; in accordance with a first embodiment of the present invention; Figure 2 shows a metal halide high-pressure discharge lamp with a tubular intermediate vessel in accordance with a second embodiment of the present invention; and Figure 3 shows a metal halide high-pressure discharge lamp in accordance with a third embodiment of the present invention, wherein the intermediate vessel is supported.

Referring now to the drawings, the 40 W highpressure discharge lamps 1, 1', 1" illustrated in Figures 1 to 3 each consist of a discharge vessel 2 pinched at one side and an encasing bulb 3, 3', 3" likewise pinched at one side, which are made of quartz glass. To electrodes 4 are sealed into the pinch 6 of the discharge vessel 2 by means of molybdenum foils 5. The current lead-in wires 7, 7', 7" of molybdenum, connected to the foils 5, serve at the same time as a holding means for the discharge vessel 2 and are sealed into the pinch 9, 9', 9" of the encasing bulb 3, 3', 3" by means of further molybdenum foils 8. The lamp 1, 1', 1", on which a base (not illustrated) is disposed, is supplied with electric current via the current lead-in wires 10 connected to these further foils 8.

The discharge vessel 2 has an internal volume of 0.2 cm3. The filli ng is composed of 0.3 mg offal, 0.75 mg ofSnl2, 0.06 mg of T11 and 8 mg of Hg.

Argon at a pressure of 100 mbar (1 x 104 Pa) is provided as ignition gas.

The space in the encasing bulb 3, 3', 3" is preferably evacuated. A getter, which is disposed on a getter holding means 11 and is sealed, free of potential, via the securing wire 12, into the pinch 6 of the discharge vessel 2 or into the pinch 9" of the encasing bulb 3", ensures the absorption of any gaseous impurities.

Because of the high pressure prevailing in the discharge vessel 2 in the operating state, it is sensible to take precautions, in the lamp 1, 1', 1", for protection against splinters in view of possible bursting of the discharge vessel 2. The encasing bulb 3, 3', 3" should also be protected from being penetrated by splinter particles. As a protection against splinters, an intermediate vessel 13,13', 13" is provided which is fused to the encasing bulb 3, 3', " In the embodiment shown in Figure 1, the intermediate vessel 13 is of dome or hood-shaped construction. It is fused to the encasing bulb 3 in the region of its apex and surrounds the discharge vessel 2 with slight spacing up to half the height of its pinch.

The embodiment shown in Figure 2 is similar two this. The intermediate vessel 13' likewise surrounds the discharge vessel 2 with slight spacing up to about half the height of its pinch - in an encasing bulb 3', the dimensions of which correspond to the encasing bulb 3 of Figure 1. In this second embodi mentofa lamp 1', the intermediate vessel 13' consists of a cylindrical portion of tube and is fused by its upper encircling edge to the inner surface of the arched end of the encasing bulb 3'.

The lamp 1" shown in Figure 3, like the lamp 1' shown in Figure 2, also comprises a tubular intermediate vessel 13" which closely surrounds the discharge vessel 2 with slight spacing and which is fused to the encasing bulb 3" by its upper encircling edge. This intermediate vessel 13", however, extends with its length beyond the pinch region of the discharge vessel 2. The current lead-in wires 7" leading to the discharge vessel 2 are bent at an angle and support the intermediate vessel 13" at its lower encircling edge. The consequence of this, however, is that the encasing bulb 3" must be larger in its dimensions in comparison wth the previous embodiments because the sealings of the current lead-in wires 7" are situated further apart.

Claims (14)

1. A high-pressure discharge lamp comprising a dscharge vessel and an encasing bulb enclosing the discharge vessel, wherein an intermediate vessel is disposed therebetween, the intermediate vessel being fused with the encasing bulb.

2. A high-pressure discharge lamp as claimed in claim 1, wherein the intermediate vessel is domeshaped and is fused with the encasing bulb at its shaped upper end.

3. A high-pressure discharge lamp as claimed in claim 1, wherein the intermediate vessel is tubular in construction and is fused with the encasing bulb at one end.

4. A high-pressure discharge lamp as claimed in claim 2 or 3, wherein current lead-in wires to the discharge vessel inside the encasing bulb are so shaped that they support the intermediate vessel at the end opposite to the fusing.

5. A high-pressure discharge lamp as claimed in any preceding claim wherein the intermediate vessel is coated.

6. A high-pressure discharge lamp as claimed in claim 5, wherein the intermediate vessel is provided with at least one IR-reflecting layer and/or at least one UV-reflecting layer.

7. A high-pressure discharge lamp as claimed in claim 5 or 6, wherein the intermediate vessel is provided with a light-diffusing layer.

8. A high-pressure discharge lamp as claimed in claim 5, 6 or 7, wherein the intermediate vessel is coated with fluorescent substance.

9. A high-pressure discharge lamp as claimed in any preceding claim, wherein the intermediate vessel is etched or sandblasted.

10. A high-pressure discharge lamp as claimed in any preceding claim wherein the intermediate vessel consists of doped glass.

11. A high-pressure discharge lamp as claimed in claim 10, wherein the intermediate vessel consists of quartz glass doped with TiO2.

12. A high-pressure discharge lamp as claimed in any preceding claim, wherein the intermediate vessel consists of coloured glass.

13. As an independent invention the additional feature of any of claims 2 to 12.

14. A discharge lamp substantially as hereinbefore described with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.